Variable area nozzle assisted noise control of a gas turbine engine

ABSTRACT

An example turbofan engine sound control system includes a core nacelle ( 12 ) housing a compressor and a turbine. The core nacelle is disposed within a fan nacelle ( 34 ). The fan nacelle includes a turbofan. A bypass flow path downstream from the turbofan is arranged between the two nacelles. A controller ( 50 ) is programmed to manipulate the nozzle exit area to control sound propagating from the engine. In one example, the controller manipulates the nozzle exit area using hinged flaps ( 42 ) to control engine sound. The hinged flaps open and close to adjust the nozzle exit area and the associated bypass flow rate.

BACKGROUND OF THE INVENTION

This invention relates to controlling noise propagating from a gasturbine engine, and, more particularly, to controlling noise byeffectively altering the nozzle exit area.

Gas turbine engines are widely known and used for power generation andvehicle (e.g., aircraft) propulsion. The engine produces engine noisedue to the airflow moving through the engine and the various movingcomponents within the engine. A person within the aircraft cabin mayhear the engine noise. A person living near to an airport may often hearengine noise from the aircraft taking off and landing at the airport.Community noise is ordinarily defined as the aircraft noise perceivableby people located on the ground in the vicinity of the airport. Enginenoise may limit an aircraft's ability to land at certain airports aftercertain hours, causing loss of revenue for an airline.

Noise from the engine primarily propagates fore and aft of the engine.The frequency content of the noise includes a tonal component and abroadband component. The fan section of the engine is a majorcontributor to overall engine noise, especially the tonal component. Thesize of the fan section relates, in part, to the desired bypass ratiofor the engine, which is the ratio of fan bypass flow to core engineflow. The trend in commercial aircraft has been to increase the bypassratio of the engine. However, increasing the bypass ratio generallyrequires increasing the size of the fan section within the turbofanengine, which may increase the noise contribution of the fan section.

What is needed is a method of optimizing engine noise for various flightconditions while maintaining engine thrust.

SUMMARY OF THE INVENTION

An example turbofan engine includes a core nacelle housing a compressor,combustor, and a turbine. A bypass flow path downstream from the fansection of the engine is a separate annular region radially outboard ofand surrounding the core. A controller is programmed to manipulate theexit area of the fan nozzle to control noise propagating from theengine. In one example, the controller manipulates the fan nozzle exitarea using hinged flaps to control engine noise. The hinged flaps openand close to adjust the nozzle exit area and the associated bypass flowrate.

Noise from the engine includes a tonal component and a broadbandcomponent. When combined with other engine parameters, such as fanspeed, modifying the effective nozzle exit area enables an operator toachieve similar thrust through the bypass flow path with differentoverall noise levels. Further, changing the effective nozzle exit areaalso alters the combination of tonal and broadband components and thenoise directivity. Depending on a flight condition, such as approach,cruise, or take-off, the overall level of engine noise can be optimized,as well as the combinations of the tonal and the broadband components.Directivity of the engine noise can also be controlled.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows.

FIG. 1 illustrates selected portions of an example gas turbine enginesystem.

FIG. 2 illustrates a variable area nozzle within the gas turbine enginesystem shown in FIG. 1.

FIG. 3 illustrates example lobes of fan noise extending from the gasturbine engine system shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A geared turbofan engine 10 is shown in FIG. 1. The engine 10 includes acore nacelle 12 that houses a low rotor 14 and high rotor 24. The lowrotor 14 supports a low pressure compressor 16 and low pressure turbine18. In this example, the low rotor 14 drives a fan section 20 through agear train 22. The fan section 20 rotates about an axis X and includes aplurality of fan blades 36. The high rotor 24 rotationally supports ahigh pressure compressor 26 and a high pressure turbine 28. A combustor30 is arranged between the high pressure compressor 26 and high pressureturbine 28. The low and high rotors 14, 24 rotate about the axis X, andat least a portion of the core nacelle 12 is disposed within a fannacelle 34. As is known, the engine 10 produces noise when running.

In the examples shown, the engine 10 is a high bypass turbofanarrangement. In one example, the bypass ratio is greater than 10:1, andthe fan diameter is substantially larger than the diameter of the lowpressure compressor 16. The low pressure turbine 18 has a pressure ratiothat is greater than 5:1, in one example. The gear train 22 can be anyknown suitable gear system, such as a planetary gear system withorbiting planet gears, planetary system with non-orbiting planet gears,or other type of gear system. It should be understood, however, that theabove parameters are only exemplary of a contemplated geared turbofanengine. That is, the invention is applicable to other types of engines,including those with direct drive fans.

For the engine 10 shown FIG. 1, a significant amount of thrust may beprovided by a bypass flow B between the core nacelle 12 and a fannacelle 34 due to the high bypass ratio. Thrust is a function ofdensity, velocity, and area. One or more of these parameters can bemanipulated to vary the amount and direction of thrust provided by thebypass flow B. In one example, the engine 10 includes a nozzle structure38 associated with the nozzle exit area A to change the physical areaand geometry to manipulate the thrust provided by the bypass flow B.However, it should be understood that the nozzle exit area A may beeffectively altered by other than structural changes, for example, byaltering a boundary layer of the bypass flow B. Furthermore, it shouldbe understood that effectively altering the nozzle exit area A is notlimited to physical locations approximate to the exit of the fan nacelle34, but rather, includes altering the bypass flow B by any suitablemeans at any suitable location.

In the example shown in FIG. 2, an engine noise control system 54includes multiple hinged flaps 42 arranged circumferentially about therear of the fan nacelle 34. The hinged flaps 42 form a portion of enginenoise control system 54, which further includes a controller 50 incommunication with actuators 46 used to manipulate the hinged flaps 42.The controller 50 also communicates with a driver 56, which may becontrolled by an aircraft operator or may operate automatically. In oneexample, the driver 56 monitors and communicates aircraft altitude andairspeed to the controller 50. Based on the combination of altitude andairspeed, the controller 50 commands the actuators 46 to actuate thehinged flaps 42 and reduce engine noise for the particular combinationof altitude and airspeed. The controller 50 thereby uses the altitudeand airspeed of the aircraft to reduce the noise level, such as toreduce the noise level perceived in a community or within an aircraftcabin. Further, different combinations of the position of the hingedflaps 42 and the rotational speed of the fan section 20 produce similaramounts of thrust. The controller 50 may command the actuators 46 toactuate the hinged flaps 42 based on the thrust and/or rotational speedmeasurement of a component of the engine 10. In so doing, the controller50 controls engine noise while maintaining a desired thrust.

The hinged flaps 42 can be actuated independently and/or in groups usingsegments 44. The segments 44 and individual hinged flaps 42 can be movedangularly using actuators 46. The engine noise control system 54 therebyvaries the nozzle exit area A (FIG. 1) between the hinged flaps 42 andthe engine 10 by altering positions of the hinged flaps 42. In a closedposition, the hinged flap 42 is closer to the core nacelle 12 for arelatively smaller nozzle exit area A. In an open position, the hingedflap 42 is farther away from the core nacelle 12 for a relatively largernozzle exit area A.

When operating, the fan section 20 of the engine 10 produces sound wavesthat propagate as lobes of fan noise N fore and aft, as shown in FIG. 3.The lobes of fan noise N include both a broadband component and a tonalcomponent. The broadband component is acoustic energy that isdistributed across a range of frequencies, whereas the tonal componentis acoustic energy focused within a narrow range of frequencies. The fansection 20 is the major contributor to the overall tonal component ofnoise propagating from the engine, although other portions of the engine10, such as the compressor 16 and turbine 18, may contribute at certainconditions. In this example, the rotating portions of the fan section 20generate the tonal component at approximately 1000 Hz. Although only fannoise N is shown in this example, many portions of the engine 10 (e.g.,the combustor 30, the rotors 14 and 24) contribute to the overall enginenoise. Each portion has an associated intensity and directivity, andeach portion is similarly modifiable with the invention. Although theexample engine 10 includes hinged flaps 42 on the fan nacelle 34, otherportions of the engine 10 may include hinged flaps 42, such as the corenacelle 12 (FIG. 1). Positioning hinged flaps 42 on the core nacelle 12may control noise from the compressors 16, 26; the combustor 30 and/orthe turbines 18, 28.

Although the engine 10 in the example embodiment produces engine noise,those skilled in the art and having the benefit of this disclosure willunderstand that engine noise is not limited to uncomfortable levels ofsound produced by the engine 10. That is, the disclosed example may beused to control various levels of sound from the engine 10.

Fan noise N extends from the engine 10 in all directions, but thehighest concentrations extend in the area of these lobes. When seated inan aircraft cabin, the directivity angle of an aircraft passengerrelative to the engine 10 is fixed. If the seated position of thepassenger is not within the fan noise N lobes, the passenger may notperceive uncomfortable levels of fan noise N from the engine 10. As anexample, a passenger seated toward the front of an aircraft cabin may bepositioned within the fan noise N lobe extending forward from the engineand, more specifically, seated at an angle of about 50 degrees relativeto the axis X. Such a passenger would experience a relatively largeamount of fan noise N within the cabin. Altering the effective nozzlearea A alters the intensity and the position of the lobes of fan noiseN. As such, the effective nozzle area A may be adjusted to direct thepeak of fan noise N away from the passenger seated toward the front ofthe cabin, as well as lessen the intensity.

Regarding the lobes of fan noise N extending rearward from the engine10, airflow communicating through the engine 10 experiences a wakedeficit, or non-uniform flow, after moving over the plurality of fanblades 36. Each fan blade 36 creates a wake deficit, or pocket of lowervelocity airflow. Stators 40, placed in the bypass flow path B,streamline the airflow and remove the swirl from the airflow through thebypass flow path B. Airflow over the stators 40 may have a vortex flowpattern, but the stators 40 straighten the airflow such that the airflowhas a substantially axial flow pattern when communicating through thenozzle exit area A.

The wake deficits from the rotating fan blades 36 cause a time-dependentvariation of pressure on the stators 40, which in turn generates thetonal component of the fan noise N propagating aft of the engine 10.Modifying the effective nozzle exit area A affects the structure of thewake deficits from the fan blades 36 and the associated fan noise N. Asa result, an operator can modify the effective nozzle exit area A tochange the associated fan noise N.

Modifying the effective nozzle exit area A increases the potentialoperating points for an engine 10 that are capable of achieving similarlevels of thrust through the bypass flow path B. As a result, theoperating point of the engine 10 can be tuned to facilitate overallnoise reduction. As an example, a typical cruising altitude for anaircraft is about 35,000 feet. Different combinations of effectivenozzle exit area A and fan section 20 speed and other engine 10parameters may produce the same desired airspeed at this altitude. As aresult, the operator is free to choose the combination of nozzle exitarea A and fan section 20 speed to control overall perceived enginenoise while maintaining required thrust. Because of the altitude,community noise is not an issue, thus the specific conditions may befurther refined to control cabin noise.

In another example, during the climbing flight stage, many sizes of theeffective nozzle exit area A produce desired thrust. Thus, the effectivenozzle exit area A can be sized to minimize noise from the engine 10.During climb, community noise remains a factor especially at loweraltitudes, thus the effective nozzle exit area may be sized to minimizethe tonal component propagating from the engine 10, as the tonalcomponent is an undesirable contributor to community noise. Thus,modifying the effective nozzle exit area A affects perceived noise fromthe engine 10 and provides a degree of freedom for designers oroperators to control noise N, and the noise level may be reduced for theparticular flight stage, e.g., take-off, climb, cruise, descent.

Although a preferred embodiment of this invention has been disclosed, aworker of ordinary skill in this art may recognize certain modificationsfalling within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope ofcoverage for this invention.

1. A turbofan engine sound control system, comprising: a core nacellehousing a compressor and a turbine; a fan nacelle housing a fan sectionthat is arranged upstream from said core nacelle; and a bypass flow pathdownstream from said fan section and arranged between said core nacelleand said fan nacelle, said bypass flow path including an effectivenozzle exit area; and a controller programmed to manipulate saideffective nozzle exit area to control sound from said engine.
 2. Theturbofan engine sound control system of claim 1, wherein said soundincludes a tonal noise component.
 3. The turbofan engine sound controlsystem of claim 1, wherein said sound includes a broadband noisecomponent.
 4. The turbofan engine sound control system of claim 1,wherein said controller manipulates said effective nozzle exit areaduring flight.
 5. The turbofan engine sound control system of claim 1,including a control device arranged to receive a command from saidcontroller in response to a flight condition, said control devicechanging said effective nozzle exit area provided between said corenacelle and fan nacelle in response to said command.
 6. The turbofanengine sound control system of claim 5, wherein said control devicechanges a physical area of said effective nozzle exit area in responseto said command.
 7. The turbofan engine sound control system of claim 5,wherein a driver communicates said flight condition to said controller.8. The turbofan engine sound control system of claim 5, wherein saidflight condition is a flight stage of said aircraft.
 9. The turbofanengine sound control system of claim 1, including at least one nozzleflap disposed on said fan nacelle operative to control said effectivenozzle exit area.
 10. A method of controlling turbofan engine sound,comprising a) generating thrust from a turbofan engine; and b) changingan effective nozzle exit area of the turbofan engine to control enginesound.
 11. A method of controlling turbofan engine sound according toclaim 10, wherein said step (b) includes changing an effective nozzleexit area while maintaining the thrust.
 12. A method of controllingturbofan engine sound according to claim 10, including c) determining adesired level of the engine sound while maintaining the thrust.
 13. Themethod of controlling turbofan engine sound according to claim 10,wherein changing the effective nozzle exit area is achieved by changinga physical area of an exit nozzle, the exit nozzle provided by aturbofan nacelle surrounding a fan section and a core nacelle.
 14. Themethod of controlling turbofan engine sound according to claim 10,wherein the engine sound level includes a tonal noise component and abroadband noise component.
 15. The method of controlling turbofan enginesound according to claim 10, wherein the engine sound level reduces atleast one of a tonal noise component and a broadband noise component.16. The method of controlling turbofan engine sound according to claim10, including: c) monitoring a position of the turbofan engine with acontroller to determine an desired engine sound level.
 17. The method ofcontrolling turbofan engine sound according to claim 10, wherein saidstep (b) includes changing the effective nozzle exit area to alter thedirectivity of the engine sound.
 18. The method of controlling turbofanengine sound according to claim 10, wherein the engine sound includes asound peak that propagates from the engine over a lobe-shape areadefined by an angle to an engine axis of rotation.
 19. The method ofcontrolling turbofan engine sound according to claim 18, wherein saidstep (b) includes changing the effective nozzle exit area to redirectthe angle of the sound peak.
 20. The method of controlling turbofanengine sound according to claim 18, wherein said step (b) includeschanging the effective nozzle exit area to redirect the lobes.
 21. Themethod of controlling turbofan engine sound according to claim 10,wherein said step (b) includes changing the effective nozzle exit areato alter thrust.
 22. The method of controlling turbofan engine soundaccording to claim 10, including: c) monitoring at least one of anairspeed or altitude.
 23. The method of controlling turbofan enginesound according to claim 22, wherein said step (b) includes changing theeffective nozzle area in response to the airspeed or altitude.